Fast Radio Bursts: SETI Implications?

byPaul GilsteronApril 1, 2015

With SETI on my mind after last week’s series on Dysonian methods, it seems a good time to discuss Fast Radio Bursts, which have become prominent this week following the appearance of a new paper. A New Scientist piece titled Is this ET? Mystery of strange radio bursts from space is also circulating, pointing out that these powerful bursts of radio waves lasting for milliseconds, each covering a broad range of radio frequencies, are still unexplained, and that they seem to follow a mathematical pattern.

Image: The 64-metre Parkes radio telescope in New South Wales (Australia), where Fast Radio Bursts of unknown origin have been detected. Credit: CSIRO Parkes Observatory.

Eleven bursts have been detected so far, dating back to 2001. The paper, by Michael Hippke (Institute for Data Analysis, Neukirchen-Vluyn, Germany), Wilfried Domainko (Max-Planck-Institut fur Kernphysik, Heidelberg) and John Learned (University of Hawaii, Manoa), points out that the pulses have dispersion measures higher than we would expect from sources inside the galaxy. But for reasons the paper goes on to explain, they’re probably not of extragalactic origin.

To untangle all this, let’s pause on the term ‘dispersion measure.’ It comes from the study of radio pulsars, where it has been observed that a pulse can be delayed depending upon its radio frequency as it sweeps through charged particles.

To clarify this, let me quote from a useful online discussion on pulsar research that Ryan Lynch (now at McGill University) published on the matter. Lynch points out that the dispersion measure (DM), which is a characteristic of a pulsar signature, doesn’t have anything to do with the pulsar itself. It is, instead, a marker that tells us something about the space between Earth and the pulsar, or as in the case above, a Fast Radio Burst. That space may contain various charged particles, but the delay they produce is inversely proportional to the mass of the particles — in other words, the amount of dispersion is dominated by electrons. According to Lynch:

These electrons disperse the pulsar’s signal… causing lower observing frequencies to arrive later than higher observing frequencies. The electrons can also scatter the signal much the same way smoke scatters visible light. The dispersion measure is a way of telling us how many electrons the signal encountered on its way to Earth. The larger the dispersion measure, the more electrons the signal encountered. This could happen for two reasons — either the pulsar is very far away, or the density of electrons in the space between Earth and the pulsar is relatively high. Both will cause an increase in the dispersion measure.

Michael Hippke and team want to consider what the dispersion measures of the detected Fast Radio Bursts tell us about their nature, hence the title of the paper, “Discrete Steps in Dispersion Measures of Fast Radio Bursts.” It’s an interesting astronomical question because it could be that FRBs could be used as ‘standard candles’ that could help us understand more about dark energy. The researchers wanted to know whether a clustering in the dispersion measure values could show which came from within our galaxy and which from without.

What turns up is what the authors describe as a ‘potential discrete spacing in DM of the FRBs.’ The bursts’ dispersion measures are integer multiples of the number 187.5, which the paper argues makes an extragalactic origin unlikely. The thinking here is that intergalactic dust would randomize the DM values, and thus we are more likely dealing with a source within the Milky Way. Just what the source could be makes for interesting speculation. From the paper:

A more likely option could be a galactic source producing quantized chirped signals, but this seems most surprising. If both of these options could be excluded, only an artificial source (human or non-human) must be considered, particularly since most bursts have been observed in only one location (Parkes radio telescope). A re-assessment of man-made phenomena, such as perytons (Burke-Spolaor et al. 2011), would then be required. Failing some observational bias, the suggestive correlation with terrestrial time standards seems to nearly clinch the case for human association of these peculiar phenomena.

That latter point has to do with the fact that FRBs seem to arrive at close to the full integer second, suggesting a man-made signal. As to the Burke-Spolaor paper cited above, it examines a series of pulses likewise detected at the Parkes instrument that are, as the abstract says, of ‘clearly terrestrial origin,’ and hence an example of our need to tune up radio-pulse survey techniques to rule out terrestrial signals. I also note the citation’s last sentence, which makes the case for a human origin. But as the Hippke paper points out, ‘In the end we only claim interesting features which further data will verify or refute.’

FRBs merit our attention because while we may have a human origin for these bursts, it’s conceivable that an extraterrestrial beacon could be in play. New Scientist quotes Jill Tarter, former director of the SETI Institute, as saying “I’m intrigued. Stay tuned.” Which we’ll all do, though mindful of the fact that with such a small number of bursts, we are working with little data. A hitherto undiscovered astronomical phenomenon would be a useful discovery, but we need to see how the pattern holds up as more FRBs are detected.

Back in 1967, The Byrds produced a song called “CTA-102,” a musical reflection of the discussion of the quasar by the same name, whose emissions had excited worldwide interest. Nikolai Kardashev himself wondered in 1963 whether a Type II or Type III civilization could be behind the then unidentified source, and subsequent observations by Gennady Sholomitskii kept the idea in the public imagination. We found a natural explanation for CTA-102, but as with FRBs, checking our data against the possibility of extraterrestrial communication makes good sense and could in the process reveal a new type of astronomical object or, more likely, a nearby human explanation.

I would have thought that the first thing to do is to confirm the observations with other radio telescopes around the world to try to eliminate terrestrial sources. I appreciate this may be difficult/expensive when dealing with rare, transient phenomena, but it is a necessary step to replicate the observations before suggesting a new phenomenon, let alone ETIs. Are any of the scopes at the Allen Array suitable/available?

One Radio Telescope is the only instrument detecting these waves?
On the off chance that the signal is aligned to the southern Hemisphere Latitude S Below 30Degs it would explain One Signal, but would not
explain subsequent signals, as the relative motion between the Emission location and Earth Receiving point would eliminate the alignment over time.
If there is nothing special about the Radio telescope this is nothing more than an interesting hunt for leakage.

The alternative is that the Transmission points are adjusting for the Earth/Solar System motion. And that has too many implications that take the whole episode way beyond a normal SETI detection.

There is in fact one FRB121102, which comes from Arecibo. All others from Parkes. Therefore, if it is interference, it must be present in both places. Man-made perytons, for example, have been found in several places.

At the end of the SETI talk, Dr. Spolaor discusses several radio bursts found by the “High Time Resolution Universe” survey which she thinks are astrophysical and distinct from the “Peryton” phenomena. The Hippke et al paper seems to propose (I welcome correction) that these are also examples of “Perytons” or similar (probably man-made) phenomena.

@NS: Yes, I think FRBs have a good chance to end up as man-made interference, coming from satellites, mobile phone base stations or god-knows-what. After the first draft of the paper, several people have proposed new tests in different fields, and we are currently doing more statistics on these. I expect an update of our paper to be published on the arXiv next week, stay tuned!

Jill Tartar no longer has any operational AUTHORITY at the Allen Telescope Array, BUT, if ATA can be reconfigured to search for fast radio bursts (at least PART of the time, I hope her power of persuasion leads to such an effort!

This is such a fascinating subject. Thank you Paul for posting this update on the FRB. I have followed the SETI research for about 20 years now. I have seen it grow and today it is a very respected research organization. I am so glad to see that during our radio/astronomy research today that it seems that there is a little more “wiggle room” for researchers to be more comfortable and speak about the possibility of ETI in their data. I truly enjoyed James Benford’s Interstellar Beacons talk.https://www.youtube.com/watch?v=te2lGSZOhT8

Slept on this and thought of something interesting. Shouldn’t interstellar beacons be located at no more than a FEW (correct me if I am wrong) light years from an inhabited planet? Assuming this IS true, one of the readers of this website’s blogs, who has either the contacts, or the skills themselves (Andrwe LePage!?) to do it should cross-reference ALL of the declinatiosn and right ascencions of the 11 FRBs with NEARBY stars whose declinations and right ascencions would put them a few light years away from a corresponding FRB, should a beacon be located at the same distance as a star. If ALL 11 FRB’s HAVE such corresponding stars, THAT WOULD ALSO BE ABOUT A ONE IN TEN THOUSAND CHANCE CO-INCIDENCE! The chances of BOTH co-incicences occurring SIMULTANEOUSLY would be ASTRONOMICAL! Shouls anyone feel this undertaking is worthy of their time, please report back to us with the results! POSITIVE results, should they occur should be FORWARDED to Tartar, et al IMMEDIATELY

There is a chance that such METI beacons might actually be placed relatively far away from the sender’s home world(s) in case any recipients turn out to be not so nice.

I could imagine advanced ETI laying out “traps” for other species via these beacons that could be their galactic competitors and either attempt to remove them or let those they capture know who is running the show.

Instead of aliens, unexpected astrophysics, or even Earthly interference, the mysterious mathematical pattern is probably an artifact produced by a small sample size, Ransom says. When working with a limited amount of data – say, a population of 11 fast radio bursts – it’s easy to draw lines that connect the dots. Often, however, those lines disappear when more dots are added.

“My prediction is that this pattern will be washed out quite quickly once more fast radio bursts are found,” says West Virginia University’s Duncan Lorimer, who reported the first burst in 2007. “It’s a good example of how apparently significant results can be found in sparse data sets.”

1. Apparently, we still don’t know what causes FRB
2. We don’t know how far (extra-galactic, galactic, terran)
3. There have been eleven of these FRB
4. Since 2007

We still can’t tell whether a signal is terran or not over after 8 years. Something is really amiss. Also, if, as some scientists believe, DM is correct and is far, far away, hopefully it’s ‘natural’.

If it is, that miniscule chance, artificial (and not terran), let me give a fun, simple example. If we shot a bunch of electrons, for a test let’s say, over a few seconds, and a microbe happened to be in the way and said ‘Ooh, what was that! Talking to me? Powerful…’ Each shot of electrons would appear, say, ‘months later’ in that little life form’s time. The energy would appear massive.

Were it really to be ET they would be doing their own thing. Not a signal for us. If it were, Hawkings is right, we do not want it to be for us (probably not anytime yet, anyway).

Take a set of enigmatic radio flashes that briefly appear across the sky, throw in a seeming uncertainty regarding their distance, and you have a first-rate astrophysical mystery at your hands. And, if the nature of this baffling phenomenon, better known as “fast radio bursts,” wasn’t enigmatic enough already, a new study comes to make it even more perplexing, by providing evidence for the existence of a possible mathematical pattern in the time delay of arrival between the various frequencies of these cosmic signals.

As described in an earlier AmericaSpace article, fast radio bursts, or “FRBs” for short, are very brief radio pulses which have been observed at various locations in the sky above and below the plain of the Milky Way galaxy. Even though they last only a few milliseconds, these enigmatic radio bursts nevertheless have an estimated energy output of up to several millions to billions of Suns during a single second, making them some the most energetic cosmic radio sources ever to be discovered.

The first FRB ever to be detected, better known as the “Lorimer burst,” was discovered quite by chance in 2007, following an extensive analysis of archival data that had been previously gathered with the 64-m Parkes radio telescope in Australia. Subsequent searches with the iconic radio telescope in the years that followed allowed scientists to uncover nine more such transient cosmic radio signals (one of which was detected almost in real-time) that seemed to be of extragalactic origin as well, helping to establish FRBs as a true astrophysical phenomenon, rather than the result of data artifacts or instrument glitches.

Finally, a team of researchers scanning the northern skies with the 305-m Arecibo radio telescope in Puerto Rico discovered a 3-milliseconds burst in the direction of the constellation Auriga, showing that FRBs weren’t a phenomenon limited to a specific area of the sky, but was widespread throughout the entire celestial sphere.

The Parkes team issued a statement a couple of days ago indicating FIVE MORE soon-to-be published FRB’s that do not come anywhere near to fitting the pattern. But, despite this, IT AINT OVER YET! Here’s why. I assume (maybe I’m wrong, but I hope not) that these five have ALL been in the pipeline for some time, but were NOT publishable until NOW for SOME REASON. Maybe that reason is that ALL FIVE were much fainter than the original ten (eleven, including the Aricibo detection). The fact is STILL that ALL of the “pattern” FRB’s are NOT of extragalactic origin. If the new five have dispersion measures indicating an INTERGALACTIC origin, we may be comparing apples and oranges, in which case, the pattern may still hold for ALL of the apples. We’ll just have to wait for the paper to come out to find out for sure.

Here’s a question. I haven’t seen any discussion of what this would mean if it’s non-natural. I don’t see any indication that there’s enough information for it to be a signal. And people keep mentioning “beacons” — but why would ET need those? Pulsars would make excellent beacons if you really need those for interstellar travel. Until there’s any indication of informational content, it’s hard to get excited about this.

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last twelve years, this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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